1. Field of the Invention
The present invention relates generally to document image scanners and more specifically to such scanners capable of performing windowing and multiple scaling.
2. Art Background
In the art of document scanning with digital technology, it is typical to scan a document by feeding the document through a data acquisition mechanism such as a charge-coupled device (CCD), which generates digitized data available for downloading to a host computer such as a PC for storage or display. FIG. 1 illustrates a prior art document scanner system in a simplified block diagram. A source document 11 is sent through CCD mechanism 100 to generate a gray scale version of the source document 11. The gray scale image is then image processed by an image-processor 110 to generate bi-tonal information to be output to the host 120 through a video bus 111. A typical application for the prior art system illustrated in FIG. 1 can be found in archiving checks in a bank, where checks are sent through the scanner at a given dot-per-inch ("dpi") resolution to allow the host computer to read the account information for further data processing purposes. Typically, the resolution of the scanned document is fixed as the data is output to the host computer 120.
FIG. 2 illustrates another typical prior art document scanner in a simplified block diagram. A source document 11 is first scanned by CCD 200 to generate data in gray scale format, which is then image processed 210 to generate a bi-tonal version of the data. It is then stored in data buffers 220 which hold multiple images. Data from data buffer 220 can be sent for data compression 230 and then to host 240 through SCSI bus 241 upon request from host 240. Although various operations are available for selecting various portions, zones, of the image stored in data buffers 220 through host 240, the resolution of the image stored in data buffers 230 is fixed.
A common problem associated with the prior art document scanners illustrated in FIGS. 1 and 2 is that a document is scanned in the same resolution by a scanner which is frequently required to perform different functions, such as OCR ("optical character recognition"), bar code reading, ICR ("intelligent character recognition"), image display, creation of an image icon, tiled compression and image storage to magnetic or optical devices. These various functions require different resolutions of the scanned document, not provided for by a single resolution scanner. Furthermore, the level of resolution is inversely proportional to the speed of the scanner, and thus the throughput of the scanner is affected. It is simply impractical for a scanner to be rescanning at different resolution when reading different portions of the document. Another problem arises when a document has a number of regions with each requiring a different resolution. For example, reading a bar code requires higher resolution than reading a simple text field. However, high resolution is not needed for archiving the entire document so that the system has to make a compromise between the amount of data that has to be stored for the entire document vs. the need for a resolution within a small area of the document.
In Telle U.S. Pat. No. 5,053,885, an electronic copier is capable of processing an image signal to, inter alia, change the magnification of a portion of an original document through its windowing and scaling modes of operation. In Marshall U.S. Pat. No. 4,628,534, a method is described for changing the horizontal and vertical resolutions of an image while the image is in digitized and compressed form. However, Marshall's scaling method aims only to maintain spatial and density integrity of the image with no regard to the edge count.
As will be appreciated by those skilled in the art, the prior art systems preclude optimizing data storage costs, system speed and read accuracies. By requiring a source document to be re-scanned for reading in a different resolution, the throughput of the scanner system is hampered. By storing a source document in a higher resolution than needed, e.g. a 300 dpi resolution for mere 100 dpi text reading, the data storage capacity of the scanner system takes a toll. Also, by indiscriminately eliminating pixels for image reduction, the scanner's read accuracy suffers. Therefore, what is needed is a document image scanner capable of scaling and windowing with intelligence all in a single scan of a document such that the goals of system throughput, storage efficiency and read accuracy are achieved.